A rubber composition prepared by using a rubber component containing only a natural rubber has been used as a rubber composition for a tread. However, in that case, since grip force of obtained tires is low, grip performance has been improved by using a synthetic rubber such as a styrene-butadiene rubber derived from petroleum resources as a rubber component in addition to the natural rubber.
However, in recent years, environmental problems have been emphasized and regulations on CO2 emission have been made rigorous. Further, since petroleum resources are finite and its supply quantity has been reduced year by year, petroleum price is predicted to surge in future and there is a limit in using raw materials derived from petroleum resources such as a styrene-butadiene rubber. Consequently, considering petroleum depletion in future, it is necessary to use resources other than petroleum such as a natural rubber and white fillers such as silica and calcium carbonate.
However, even if non-petroleum resources are used, equal or better tread performances (for example, grip performance of a tire) are required compared with performances of conventional treads obtained by use of petroleum resources.
In order to improve performance of a tread portion of a tire by using non-petroleum resources, JP2002-533234A discloses a process for preparing a rubber composition for a tire containing, as a rubber component, an epoxidized natural rubber, which is a non-petroleum resource. However, although grip performance is not inferior as compared with a tire using petroleum resources, rolling resistance cannot be adequately reduced. Thus, reduction of rolling resistance is further required, considering influence on environment.